This application is based upon and claims benefit of priority of Japanese Patent Application No. 2002-216041 filed on Jul. 25, 2002, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a starter for cranking an internal combustion engine, the starter having a magnetic switch that includes a main switch and an auxiliary switch.
2. Description of Related Art
An example of a conventional starter for cranking an internal combustion engine is shown in FIG. 5. The starter is composed of an electric motor and a magnetic switch. An input terminal of the starter is connected to an on-board battery. Upon turning on a key-switch, a relay is closed and thereby the magnetic switch is energized. When the magnetic switch is energized, a pinion of the starter is pushed toward a ring gear of the engine and engaged therewith. At the same time, electric current is supplied to the electric motor by closing electric contacts connected to the input terminal. Thus, rotational torque of the electric motor is transferred to the engine through the pinion to thereby crank up the engine.
As shown in FIG. 5, the conventional starter has two terminals, i.e., the input terminal connecting the electric motor to the on-board battery and a switch terminal connecting a magnetic coil of the magnetic switch to the relay. In other words, the starter has to be connected to outside circuits through two lead wires led out from the starter. It is desirable and convenient if the starter could be electrically connected to the circuit of a vehicle with a single lead wire.
To realize the single wire connection, a German patent document DE-10047288-A1 proposes to remove the magnetic switch from the starter and to operate the starter as a mere electric motor in a controlled manner. This proposal, however, involves some problems. To smoothly crank up the engine, a rotational torque of the electric motor has to be transferred to the pinion gear after the pinion gear surely engages with the ring gear of the engine. On the other hand, the pinion gear has to be quickly disengaged from the ring gear after the engine is cranked up. That is, operation of the electric motor has to be well synchronized with the engagement of the pinion gear with the ring gear. This synchronized operation is usually realized by the magnetic switch installed in the starter together with the electric motor. Since the magnetic switch is not included in the starter proposed by DE-10047288-A1, cranking operation of the starter cannot be performed in a sufficiently synchronized manner.
Another example of the single wire starter is a starter for use in a motorcycle. This type of the starter has no magnetic switch for establishing engagement between the pinion gear and the ring gear. The pinion gear is engaged with the ring gear by its inertia (so-called Bendix-type engagement). It has been well known that this type of engagement cannot be perfect. As exemplified above, so-called one-wire starters have not been perfect in their operation and reliability.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved starter that is electrically connected by means of a single wire without sacrificing its reliability.
A starter for cranking an internal combustion engine includes an electric motor, a pinion gear driven by the electric motor, and a magnetic switch for engaging the pinion gear with a ring gear of the engine and for energizing or de-energizing the electric motor. The starter also includes an input terminal connected to an on-board battery through a relay operated by a key-switch. Electric power fed to a magnetic coil of the magnetic switch and electric power fed to the electric motor are commonly supplied from the single input terminal connected to the on-board battery.
The magnetic switch includes a plunger driven by the magnetic coil, a main switch and an auxiliary switch. Both the main switch and the auxiliary switch are turned on and off in response to movement of the plunger. Both switches are connected in parallel to each other and disposed between the input terminal and the electric motor. The auxiliary switch includes an electric resistor for restricting amount of current supplied to the electric motor. The electric resistor may be formed in a stationary contact of the auxiliary switch, the stationary contact being made of a carbon material. The main switch includes no resistor so that a full current is supplied to the electric motor when the main switch is closed.
Upon turning on the key-switch, the magnetic coil in the magnetic switch is energized. Upon energizing the magnetic coil, the plunger is driven and the auxiliary switch is closed by the plunger, and a limited amount of current is supplied to the electric motor, thereby rotating the electric motor at a low speed. At the same time, the pinion gear is engaged with the ring gear in response to the movement of the plunger. This engagement may be established by pushing the pinion gear toward the ring gear while stopping rotation of the pinion gear. As the plunger is further driven, the main switch is closed, and thereby a full amount of electric current is supplied to the electric motor. The pinion gear engaging with the ring gear is fully driven by the electric motor, and the engine is cranked up. After the engine is cranked up, the key-switch is turned off to terminate power supply to the starter.
The main switch may be constituted by a stationary contact and a movable contact. Alternatively, it may be constituted by utilizing a contact between a commutator of the electric motor and brushes slidably contacting the commutator. In this case, the brushes are separated from the commutator when the starter is not in operation, and the contact therebetween is established by the movement of the plunger of the magnetic switch.
According to the present invention, the starter that is able to be electrically connected to an on-board system with a single wire is realized without sacrificing functions of the magnetic switch. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.